I'm having success now, even with longer jumpers; the fix seemed to come from sending 0xFF instead of 0x00 after READ commands. I really don't know why that should affect performance.. data sheet claims it's a don't-care.I'm away from my board right now, but I'm going to write a conclusive test case (ie write and read 0-255 and compare for errors) before wrapping up the topic and summarizing changes. But I hope it's done!